It is all a bit odd.
However, I think the idea she was abducted or there was foul play is really unlikely.
It feels like there were too many people around, (other dog walkers, etc) in broad daylight. That combined with the fact that there couldn't have been a vehicle anywhere near where she disappeared, if someone had abducted/murdered her, they'd have to have man-handled her all the way to a vehicle or somewhere out of sight, it doesn't really add up.
If somebody wanted her dead, or whatever - there would have far more practical and sensible ways to achieve it, than in broad daylight in a public area..
I suspect she did fall in, with the clothes she was wearing and the fact she probably wasn't used to swimming in cold water, meant she had little to no chance.